Hydrogen peroxide vaporizer

ABSTRACT

An apparatus for decontaminating articles comprised of:
         a decontamination chamber; a conveyor for conveying articles to be decontaminated along a first path through the decontamination chamber;   a vaporizing unit connected to the decontamination chamber, the vaporizing unit disposed above the decontamination chamber;   a blower for conveying a carrier gas through the vaporizing unit and through the decontamination chamber;   heating means for heating the carrier gas flowing through the vaporizing unit;   a source of liquid hydrogen peroxide fluidly connected to the vaporizing unit; and   an injection device for injecting liquid hydrogen peroxide into the vaporizing unit.

FIELD OF THE INVENTION

The present invention relates to the generation of vaporized hydrogenperoxide, and more particularly, to a system for generating largeamounts of vaporized hydrogen peroxide and a method of operating thesame.

BACKGROUND OF THE INVENTION

It is known to use hydrogen peroxide (H₂O₂) in sterilization and otherprocesses. In a sterilization process, liquid hydrogen peroxide isvaporized to form vaporized hydrogen peroxide (VHP). The vaporizedhydrogen peroxide is typically produced from a liquid mixture ofhydrogen peroxide and water. Care must be taken when vaporizing thismixture due to the difference in the boiling points between water andhydrogen peroxide. In this respect, water boils at 100° C., whereas purehydrogen peroxide boils at 150° C. Accordingly, when a mixture of waterand hydrogen peroxide is vaporized, the water tends to boil before thehydrogen peroxide unless the mixture is flash vaporized. In conventionalsystems, flash vaporization is accomplished by dripping a small amountof the water and the hydrogen peroxide mixture on a hot surface. Air isdirected over the hot surface to conduct away the vaporized hydrogenperoxide.

U.S. Pat. No. 2,491,732 discloses a conventional vaporized hydrogenperoxide (VHP) vaporizer. A problem with the aforementioned drip methodof vaporization is that a hot surface must be maintained to vaporize theliquid hydrogen peroxide and water mixture. Testing has shown that aninjection rate of up to 5 grams per minute per injection port can beachieved with current drip-method vaporizers. At higher injection rates,individual droplets can no longer be maintained. In other words, thedrip-type vaporizer is limited in the amount of vaporized hydrogenperoxide it can produce within given size limits. This limitationprevents drip-type vaporizers from being used in certain high volumesterilizing processes where it is necessary to sterilize large numbersof articles and devices in a short period of time.

Another problem with vaporized hydrogen peroxide decontamination systemsis preventing condensation of the vaporized hydrogen peroxide on thearticles or surfaces to be decontaminated.

It is therefore desirable to have a high-capacity vaporized hydrogenperoxide generator capable of generating high volumes of vaporizedhydrogen peroxide at concentration levels that will not condensate onthe articles or surfaces to be decontaminated.

The present invention provides a hydrogen peroxide vaporizer capable ofgenerating large volumes of vaporized hydrogen peroxide at concentrationlevels that will not condensate on the articles or surfaces to bedecontaminated.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention,there is provided an apparatus for decontaminating articles comprised ofa decontamination chamber. A conveyor conveys articles to bedecontaminated along a first path through the decontamination chamber. Avaporizing unit connects to the decontamination chamber. The vaporizingunit is disposed above the decontamination chamber. A blower conveys acarrier gas through the vaporizing unit and through the decontaminationchamber. A heating means heats the carrier gas flowing through thevaporizing unit. A source of liquid hydrogen peroxide fluidly connectsto the vaporizing unit. An injection device injects liquid hydrogenperoxide into the vaporizing unit.

In accordance with another aspect of the present invention, there isprovided an apparatus for decontaminating articles in a decontaminationchamber having a reservoir assembly comprised of a first storage tankconnected to a source of hydrogen peroxide, and a second storage tankconnects to a source of hydrogen peroxide. A collection tank isconnected to the first storage tank and the second storage tank toreceive hydrogen peroxide therefrom. The collection tank also connectsto a vaporizing unit. A valve means selectively fluidly communicates thefirst storage tank and the second storage tank with the collection tank.The valve means also selectively fluidly communicates the first storagetank and the second storage tank with the source of liquid hydrogenperoxide. A vent line has one end connected to the collection tank. Asecond end of the vent line is disposed at a location above a top of thefirst storage tank and the second storage tank. A vent valve is disposedin the vent line to control flow therethrough.

An advantage of the present invention is a high-capacity vaporizedhydrogen peroxide (VHP) generator.

Another advantage of the present invention is a decontamination systemcapable of producing large quantities of vaporized hydrogen peroxide.

Another advantage of the present invention is a decontamination systemas described above having several methods for confirming the flow ofvaporized hydrogen peroxide through the system.

Another advantage of the present invention is a decontamination systemas described above that is capable of modifying the flow of carrier gastherethrough.

Another advantage of the present invention is a decontamination systemas described above that is capable of modifying the injection rate ofliquid sterilant into the system.

Another advantage of the present invention is a decontamination systemas described above that is capable of modifying the temperature of acarrier gas flowing therethrough.

Another advantage of the present invention is a decontamination systemas described above that operates to maintain the concentration ofvaporized hydrogen peroxide in a carrier gas at a level wherein thevaporized hydrogen peroxide has a dew point below the initialtemperature of articles to be decontaminated.

A still further advantage of the present invention is a decontaminationsystem as described above wherein system components are arranged suchthat unvaporized hydrogen peroxide (if present) will flow downwardthrough a system to be collected at a low point in the system.

Another advantage of the present invention is a decontamination systemas described above having a sterilant supply system with a settling tankto eliminate entrained or trapped gas in a sterilant supply line to avaporizer.

Another advantage of the present invention is a decontamination systemas described above having an air process unit for filtering and dryingair used within the system.

Another advantage of the present invention is a method of operating asystem as described above to prevent condensation on articles orsurfaces to be decontaminated.

Another advantage of the present invention is a method of operating asystem as described above to maintain a desired concentration ofvaporized hydrogen peroxide at the location where articles or surfacesare to be decontaminated.

Another advantage of the present invention is a method of operating asystem as described above to maintain a fixed injection rate of liquidsterilant.

These and other advantages will become apparent from the followingdescription of a preferred embodiment taken together with theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthe specification and illustrated in the accompanying drawings whichform a part hereof, and wherein:

FIG. 1 is a drawing schematically illustrating a high-capacity vaporizedhydrogen peroxide decontamination system, illustrating a preferredembodiment of the present invention;

FIG. 2 is a drawing schematically illustrating a sterilant supply unitfrom the decontamination system shown in FIG. 1;

FIG. 3 is a drawing pictorially illustrating a vaporizer unit from thedecontamination system shown in FIG. 1;

FIG. 4 is a drawing schematically illustrating an aeration unit from thedecontamination system shown in FIG. 1;

FIG. 5 is a drawing schematically illustrating an air conditioning unitfrom the decontamination system shown in FIG. 1;

FIG. 6 is a drawing schematically illustrating a destroyer unit from thedecontamination system shown in FIG. 1;

FIG. 7 is a sectional view of a vaporizer from the decontaminationsystem shown in FIG. 1;

FIG. 8 is an enlarged view of an atomizer from the vaporizer unit shownin FIG. 7;

FIG. 9 is a perspective view of a manifold and decontamination chamber;

FIG. 10 is a graph of a heat of vaporization (latent heat) as a functionof a concentration of hydrogen peroxide in water;

FIG. 11 is a graph of density of hydrogen peroxide as a function of aconcentration of hydrogen peroxide in water; and

FIG. 12 is a graph of a heat capacity of hydrogen peroxide as a functionof a concentration of hydrogen peroxide in water.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only, and notfor the purpose of limiting same, FIG. 1 shows a vaporized hydrogenperoxide decontamination system 10 for continuously decontaminatingarticles 12 moving along a conveyor belt 14, illustrating a preferredembodiment of the present invention.

Broadly stated, a decontamination system 10, according to the presentinvention, is comprised of a sterilant supply unit, an air conditioningunit, a vaporizer unit, a decontamination room or isolator, a destroyerunit and an aeration unit. In the embodiment shown, decontaminationsystem 10 includes a single sterilant supply unit 100, a single airconditioning unit 200, two vaporizer units 300A, 300B, twodecontamination rooms 500A, 500B, two destroyer units 600A, 600B and twoaeration units 700A, 700B.

Sterilant Supply Unit 100

Referring now to FIG. 2, sterilant supply unit 100 is best seen. Asupply line 112 connects sterilant supply unit 100 to an external supply114 of liquid sterilant. A pump and drain assembly 120 is connected tosupply line 112. Pump and drain assembly 120 includes a pump 122 drivenby a motor 124. Pump 122 and motor 124 are designed to convey meteredamounts of liquid sterilant to a reservoir assembly 130.

Reservoir assembly 130 preferably includes two reservoir tanks 132A,132B. Two sterilant holding tanks 132A, 132B are provided to allowcontinuous, uninterrupted flow of sterilant to vaporizer units 300A,300B. In this respect, one holding tank 132A may be filled withsterilant, while the other tank 132B is being used to provide sterilantto vaporizer units 300A, 300B, as shall be described in greater detailbelow. Tanks 132A, 132B are essentially identical, and therefore, onlytank 132A shall be described in detail. It being understood that thedescription of tank 132A applies to tank 132B.

Tank 132A is generally columnar in shape, and is comprised of a tubularshell or wall 134 having a base 136 and a cover 138 at the ends thereof.In a preferred embodiment, tubular shell 134 is cylindrical in shape andis formed of a translucent material. Tank 132A defines an inner chamber142 for holding a liquid sterilant S. Supply line 112 is connected toreservoir tanks 132A, 132B by branch supply lines 112 a, 112 b. Valves144, 146 are disposed respectively in branch supply lines 112 a, 112 bto control flow of liquid sterilant S to reservoir tanks 132A, 132B.Each tank 132A, 132B includes level sensor 154. Sensor 154 is providedto indicate an “overfill level,” as shall be described in greater detailbelow. A pressure sensor 155 is provided at the bottom of each tank132A, 132B to provide pressure signals that are indicative of the levelof fluid in each tank 132A, 132B.

Tanks 132A, 132B are connected at their bottom ends to a holding tank170 by fluid conduits 162, 164, respectively. Control valves 166, 168are disposed respectively in fluid conduits 162, 164 to control the flowof sterilant from reservoir tanks 132A, 132B to holding tank 170. Theupper ends of reservoir tanks 132A, 132B are connected to a vent line158, as schematically illustrated in FIG. 2.

Holding tank 170 defines air enclosed holding chamber 172. A vent line174 extends upwardly from holding chamber 172. A control valve 176 isdisposed within vent line 174 to control flow therethrough. As best seenin FIG. 2, vent line 174 has a length such that the upper end of ventline 174 is disposed at the upper ends of reservoir tanks 132A, 132B. Alevel sensor 177 is disposed within holding chamber 172 of holding tank170 at a predetermined level. A level sensor 177 is disposed withinholding tank 170. In the embodiment shown, level sensor 177 is a floatswitch.

A fluid conduit 184 extending from the bottom of holding tank 170connects holding chamber 172 to a control valve 186 that regulates flowof sterilant from holding tank 170 to either a vaporizer feed line 192or to a drain line 194 that is connected to supply line 112. Asillustrated in FIG. 2, drain line 194 is in fluid communication withdrain line 126 of pump and drain assembly 120. A return line 196 extendsfrom vaporizer feed line 192 to the top of tank 132A. A control valve198 is disposed within return line 196 to control the flow of sterilanttherethrough.

Vaporizer feed line 192 is connected to vaporizer unit 300A andvaporizer unit 300B, as illustrated in the drawings. Sterilant fromholding tank 170 is preferably fed by gravity to vaporizer units 300A,300B. Accordingly, in the embodiment shown, holding tank 170 andreservoir tanks 132A, 132B are disposed above vaporizer units 300A,300B, i.e., at a higher elevation.

Air Conditioning Unit 200

Referring now to FIG. 5, the air conditioning unit 200 is bestillustrated. Air conditioning unit 200 is provided to condition, i.e.,to filter and to dry air used in vaporizer units 300A, 300B, and tofilter air used by aeration units 700A, 700B. Air conditioning unit 200is basically comprised of a filter 222, a cooling assembly 230 and adesiccant wheel 242 arranged in series.

An air inlet conduit 212 has a first end 212 a that communicates withthe environment, namely room air. Another end 212 b of air inlet conduit212 is connected to chamber 262 within air conditioning unit 200. Filter222 is disposed within air inlet conduit 212 to filter air flowingtherethrough. Filter 222 is preferably a HEPA filter. Cooling assembly230 is disposed downstream from filter 222. Cooling assembly 230 iscomprised of a cooling coil 232 and a chiller 234 that is connected tocooling coil 232. Cooling coil 232 surrounds air inlet conduit 212.Chiller 234 is dimensioned to provide sufficient cooling to coil 232surrounding air inlet conduit 212 such that air flowing through airinlet conduit 212 is chilled to precipitate moisture within the air. Inother words, chiller 234 has sufficient capacity to dehumidify airflowing through air inlet conduit 212. Between filter 222 and coolingcoil 232, an air supply line 214 is connected to air inlet conduit 212.Air supply line 214 provides filtered air throughout system 10 to coolelectronics (not shown). A second air supply line 216 is connected toair inlet conduit 212 between filter 222 and cooling coil 232. Secondair supply line 216 provides filtered air to aeration units 700A, 700B,as shall be described in greater detail below. Desiccant wheel 242,rotatable about a first axis “A,” is disposed at end 212 b of air inletconduit 212, i.e., downstream from filter 222 and cooling coil 232.Desiccant wheel 242 is disposed such that half of wheel 242 rotates intochamber 262. End 212 b of air inlet conduit 212 directs air flow throughthat portion of desiccant wheel 242 that is positioned within chamber262. Desiccant material within desiccant wheel 242 is operable to absorbmoisture in the air flowing through air inlet conduit 212. Thus, airentering chamber 262 has been filtered and dried by means of filter 222,cooling coil 232 and desiccant wheel 242. A humidity sensor 272 and atemperature sensor 274 are disposed within chamber 262 to monitorrespectively the humidity and temperature of the air within chamber 262.Chamber 262 is in fluid communication with vaporizer units 300A, 300Bvia air line 282, as illustrated in FIG. 5.

Air conditioning unit 200 includes a regeneration system 290 forregenerating, i.e., removing moisture from, desiccant wheel 242. Aregeneration conduit 292 is connected to chamber 262. A blower 294,driven by a motor 296, draws dried and filtered air within chamber 262and directs the dried air through a heater 298 that heats the dry air.Regeneration conduit 292 is arranged to direct the heated, dried,filtered air through that portion of desiccant wheel 242 that is outsideof chamber 262. As will be appreciated by those skilled in the art, theheated air dries, i.e., removes moisture from desiccant wheel 242. Moistair flowing from desiccant wheel 242 through regeneration conduit 292flows out of air conditioning unit 200 through an orifice 284. Apressure transducer 285 is disposed at the outlet, i.e., downstream, ofblower 294. Pressure transducer 285, in conjunction with orifice 284, isused to establish a desired air flow through conduit 292, to ensureproper moisture removal. A temperature sensor 286 monitors thetemperature of the air exiting heater 298. The temperature in conduit292 is controlled to ensure proper moisture removal.

Vaporizer Units 300A, 300B

Referring now to FIGS. 3, 7, 8 and 9, vaporizer units 300A, 300B arebest seen. Vaporizer units 300A, 300B are essentially identical, andtherefore, only vaporizer unit 300A shall be described in great detail,it being understood that such description applies equally to vaporizerunit 300B. As illustrated in FIG. 3, vaporizer unit 300A (and vaporizerunit 300B) is connected to vaporizer feed line 192 from sterilant supplyunit 100, and is connected to air line 282 from air conditioning unit200.

Vaporizer unit 300A is comprised of a blower 322, a flow element 332 formeasuring airflow, a heater 352 and a vaporizer 360, that are allschematically illustrated in FIG. 3, and pictorially illustrated in FIG.7.

In the embodiment shown, vaporizer unit 300A includes a cabinet orhousing 312 mounted on a structural steel support frame 314. Cabinet 312and support frame 314 together define an upright, columnar structure. Ablower 322 is disposed at a bottom location of support frame 314. Blower322 is driven by a motor 324. Motor 324 is preferably a variable speedmotor, wherein the output of blower 322 can be controlled to increaseair flow therethrough. The inlet of blower 322 is connected to air line282 from air conditioning unit 200. When in operation, blower 322 drawsair through air conditioning unit 200 where the air is then dried andfiltered. In the embodiment shown, the outlet of blower 322 is connectedto a vertical conduit 328. A flow element 332 is disposed within conduit328 to measure air flow through conduit 328. Flow element 332 ispreferably a Venturi device. A sensor 334 measures a pressure differenceacross the Venturi device and provides a signal indicative of the airflow through flow element 332. A Venturi device is preferable because ofthe high resolution of air flow it can provide and because of the lowloss of power for the air flowing therethrough. A pressure sensor 335 isprovided to measure the static pressure to flow element 332, tofacilitate calculation of the mass air flow rate through conduit 328, asshall be described in greater detail below. A temperature sensor 336 isdisposed downstream from flow element 332.

In the embodiment shown, a generally U-shaped conduit section 342 isconnected to flow element 332 to redirect the flow of air. Conduitsection 342 includes an elongated straight heater section 342 a that isvertically oriented in the embodiment shown. As illustrated in FIG. 7,the passageway defined by conduit section 342 increases in across-sectional area from the end of conduit section 342, that connectsto flow meter 332, to elongated straight heater section 342 a. A heatingelement 352 is positioned within straight heater section 342 a ofconduit section 342 and is provided to heat the air flowing throughconduit section 342. In the embodiment shown, heating element 352 is anelectrical device. An insulating layer 354 surrounds and enclosesheating element 352. Heating element 352 is designed to be capable ofheating air flowing through conduit section 342 up to a temperature highenough to vaporize hydrogen peroxide and high enough to maintain adesired temperature sufficient to prevent condensation indecontamination system 10. In one embodiment, heating element 352 iscapable of heating air flowing through conduit section 342 to at leastabout 105° C. In another embodiment, heating element 352 is capable ofheating air flowing through conduit section 342 to at least 180° C. Theincrease in the cross-sectional area of conduit section 342 allows thesmaller piping from flow element 332 to connect to the larger diameterof heater section 342 a.

A vaporizer 360 is connected to the end of conduit section 342downstream from heater 352. Vaporizer 360 is comprised of a housing 362defining an elongated inner vaporizing plenum 364. In the embodimentshown, housing 362 is comprised of a rectangular shell 366 having afirst end 366 a having a flat cap 372 thereon, and a second end 366 bhaving a funnel-shaped base 374. The cross-sectional area and the lengthof housing 362 are dimensioned to allow sufficient time for the liquidsterilant to be vaporized therein. First end 366 a of vaporizer 360defines an inlet end, and second end 366 b of vaporizer 360 defines anoutlet end. Shell 366, cap 372 and base 374 are preferably formed ofmetal, and more preferably, of aluminum. Cap 372 is secured to shell366, preferably by welding. Conduit section 342 communicates with innerplenum 364 of vaporizer 360 through an opening in cap 372. Outlet end366 b of shell 366 includes an annular flange 376 for connecting to anannular flange 378 on base 374. Base 374 is funnel-shaped and connectsvaporizer housing 362 to a vaporized hydrogen peroxide feed line 512Athat in turn is connected to decontamination chamber 500A.

As illustrated in FIG. 7, vaporizer 360 is oriented such that theelongated vaporizer plenum 364 is vertically oriented. In this respect,heating element 352 and straight section 342 a of conduit section 342are vertically aligned with vaporizer plenum 364 so as to direct heatedair downwardly through vaporizer plenum 364.

A sterilant injection system 410 is disposed within vaporizer plenum364. Injection system 410 is centrally disposed within plenum 364, andis oriented to inject sterilant into plenum 364 in a downwardlydirection toward second end 366 b of vaporizer housing 362.

Injection system 410, best seen in FIG. 8, is comprised of a tubularbody 412 that defines an inner mixing chamber 414. An air line 422 and asterilant line 424 connect to body 412 and communicate with inner mixingchamber 414. Air line 422 is connected to a source (not shown) offiltered, dry pressurized air within system 10 by conduit 423. Sterilantline 424 is connected to sterilant supply line 192 from sterilant supplyunit 100. A pump 426, driven by a motor 428, schematically illustratedin FIG. 3, is disposed in sterilant supply line 192 to feed sterilantunder pressure into injection system 410. Pump 426 is preferably avariable-speed peristaltic pump. Pump 426 is provided to pump sterilantinto injection system 410 at a selected rate. (The injection rate ingrams per minute is measured by a mass meter 427.) Motor 428 ispreferably a variable speed motor wherein the injection rate ofsterilant to injection system 410 can be varied by the speed of motor428. A pressure sensor 429 is disposed in sterilant supply line 192,downstream from pump 426. Pressure sensor 429 monitors (and ensures)proper sterilant injection rate and ensures that the injection system410 does not become obstructed.

An atomizing nozzle 432 is attached to body 412. Nozzle 432 ispreferably capable of creating a fine spray of sterilant, i.e., namely amist that is sufficiently small to ensure complete vaporization. Acommonly available atomizing nozzle finds advantageous application inthe present invention.

To facilitate positioning injection system 410 within vaporizer plenum364, an opening 438 is formed in the side of shell 366. A collar 442 isattached, preferably by welding, to shell 366 to surround opening 438. Acover plate 444 is attached to collar 442 with conventional fasteners446. A gasket 467 is disposed between cover plate 444 and collar 442 toprovide a complete seal. Threaded openings in cover plate 444 receiveconventional fittings 448 that connect air line 422 to an air conduit423, and sterilant line 424 to sterilant supply line 192.

According to one aspect of the present invention, nozzle 432 isdimensioned relative to shell 366 such that contact of spray from nozzle432 with shell 366 is minimized or avoided during operation of vaporizer360.

A temperature sensor 452 is disposed within vaporizer plenum 364 betweenfirst end 366 a of vaporizer 360 and sterilant injection system 410. Asecond temperature sensor 454 is disposed within vaporizer plenum 364downstream from sterilant injection system 410 near second end 366 b ofvaporizer housing 362. The temperature drop between sensors 452, 454 isproportional to the heat necessary to vaporize the sterilant, as shallbe discussed in greater detail below.

A vaporized hydrogen peroxide sensor 462, that is capable of providingan indication of the concentration of vaporized hydrogen peroxide andwater vapor, is optionally disposed within vaporizer plenum 364downstream from sterilant injection system 410. Vaporized hydrogenperoxide sensor 462 is disposed near second end 366 b (the outlet end)of vaporizer 360. Sensor 462 is preferably an infrared (IR) sensor, andmore preferably a near infrared (IR) sensor. Sensor 462 is generallycylindrical in shape, and is mounted in housing 362 to traverse plenum364. Sensor 462 is mounted to housing 362 to be easily removabletherefrom.

Decontamination Chambers 500A, 500B

As illustrated in FIG. 1, vaporizer unit 300A, 300B are connectedrespectively to decontamination chambers 500A, 500B by vaporizedhydrogen peroxide conduits 512A, 512B. Decontamination chambers 500A and500B are essentially identical, and therefore, only decontaminationchamber 500A shall be described, it being understood that suchdescription applies equally to decontamination chamber 500B.

Decontamination chamber 500A, best seen in FIGS. 6 and 9, is comprisedof an enclosure or housing 522 that defines a space or region 524through which articles 12 to be sterilized/decontaminated are conveyedby conveyor 14. A manifold 542 is mounted on housing 522, and has aplurality of spaced-apart openings or nozzles 544 that communicate withspace or region 524 in housing 522. As best seen in FIG. 9, nozzles 544are disposed above conveyor 14 to uniformly distribute vaporizedhydrogen peroxide over articles 12 moving through decontaminationchamber 500A.

As best seen in FIG. 9, a temperature sensor 546 and a vaporizedhydrogen peroxide sensor 552 are disposed within manifold 542. Vaporizedhydrogen peroxide sensor 552 is capable of providing an indication ofthe concentration of vaporized hydrogen peroxide and water vapor, Sensor552 is preferably a near infrared (IR) sensor. Sensor 552 is cylindricalin shape and has fiber optic cables 552 a extending therefrom. Tofacilitate easy insertion and removal of near infrared sensor 552 frommanifold 542, a pair of spaced-apart rails 562, 564 extend throughmanifold 542. In the embodiment shown, rails 562, 564 are cylindricalrods. Near infrared sensor 552 is inserted through the opening in thesides of manifold 542. Caps or plugs 572 that allow cables 552 a toextend therethrough seal the openings.

Destroyer Units 600A, 600B

Referring now to FIG. 6, destroyer units 600A and 600B are schematicallyillustrated. Destroyer unit 600A and destroyer unit 600B are essentiallyidentical, and therefore, only destroyer unit 600A shall be described,it being understood that such description applies equally to destroyerunit 600B.

A conduit 612 connects enclosure 522 to destroyer unit 600A. As bestseen in FIG. 9, a conduit 612 communicates with region 524 in enclosure522 through one side of enclosure 522. A flow measuring device 622 isdisposed within conduit 612 to provide data with respect to flowtherethrough. In the embodiment shown, flow measuring device 622includes a pressure sensor 624 that is operable to sense a pressuredifference across flow measuring device 622 and to provide a signalindicative of flow through device 622. In a preferred embodiment, flowmeasuring device 622 is a Venturi device. An additional pressure sensor625 is provided to measure static pressure in the flow measuring device622, for mass flow calculations as shall be discussed below. Atemperature sensor 626 is disposed within conduit 612 downstream fromflow measuring device 622. Conduit 612 is connected to the inlet end ofa blower 632 that is driven by a motor 634. A conduit 636 extending fromthe outlet side of blower 632 is connected to a destroyer 642. Destroyer642 is basically a catalytic device that is operable to destroy hydrogenperoxide flowing therethrough. In this respect, catalytic destroyersconvert the vaporized hydrogen peroxide into water and oxygen. Atemperature sensor 662 is disposed in front, i.e., upstream, ofdestroyer 642. A second sensor 664 is disposed behind, i.e., downstream,from destroyer 642.

Aeration Units 700A, 700B

Referring now to FIG. 4, aeration unit 700A is schematicallyillustrated. Aeration unit 700A and aeration unit 700B are essentiallyidentical, and therefore, only aeration unit 700A shall be described, itbeing understood that such description applies equally to aeration unit700B. As illustrated in FIG. 4, aeration unit 700A is connected to airsupply line 216 from air conditioning unit 200. Air supply line 216 fromair conditioning unit 200 supplies filtered air to aeration units 700A,700B. Air supply line 216 is connected to the inlet side of a blower 712that is driven by a variable-speed motor 714. Blower 712 is disposedwithin aeration unit 700A to draw air external to system 10 throughfilter 222 in air conditioning unit 200 and through supply line 216. Theoutlet side of blower 712 is connected to an aeration conduit 722.Aeration conduit 722 extends through aeration unit 700A. Downstream fromblower 712, a flow measuring device 732 is disposed within aerationconduit 722. In a preferred embodiment, flow measuring device 732 is aVenturi device. A pressure sensor 734 measures the pressure differenceacross flow measuring device 732 that provides signals indicative of theflow through aeration conduit 722. A pressure sensor 735 is provided tomeasure the static pressure to flow measuring device 732, to facilitatecalculation of the mass flow rate through aeration conduit 722. Atemperature sensor 736 is disposed before (upstream of) flow measuringdevice 732. Temperature sensor 736 is disposed between blower 712 andflow measuring device 732. A valve element 738 is disposed in aerationconduit 722 downstream from flow measuring device 732 to regulate theamount of flow through aeration conduit 722. A filter element 742 isdisposed downstream from valve element 738. Filter element 742,preferably a HEPA filter, provides a second filtration of the airflowing through aeration conduit 722, in addition to filter 222 in airconditioning unit 200. A heating element 752 is disposed in aerationconduit 722 downstream from filter element 742. Manifold 762 includes aplurality of nozzles or ports 764 to distribute the filtered and heatedair into chamber 500A. Manifold 762 is disposed above conveyor 14 at alocation where conveyor 14 exits decontamination chamber 500A. Atemperature sensor 766 is disposed within manifold 762.

Aeration unit 700A basically provides heated, filtered air todecontamination chamber 500A to purge peroxide vapor from articles 12 onconveyor 14 and to prevent condensation.

As best seen in FIGS. 1 and 4, a conduit 772 connects vaporized hydrogenperoxide conduit 512A to aeration conduit 722. Conduit 772 is connectedto vaporized hydrogen peroxide conduit 512A between vaporizer 360 andmanifold 542. Conduit 772 is connected to aeration conduit 722 betweenvalve 738 and filter element 742. A valve 774 is disposed in conduit 772to control flow therethrough. Conduit 772 is provided to periodicallydecontaminate filter element 742 in aeration unit 700A. By closing valve738 in aeration conduit 722 and by opening valve 774 in conduit 772,vaporized hydrogen peroxide can be directed from vaporizer 360 throughfilter element 742.

As provided in the present invention, by controlling the airtemperature, air flow rate, sterilant temperature and sterilantinjection rate in a decontamination system, a desired concentration ofvaporized hydrogen peroxide can be maintained within a decontaminationchamber. When using vaporized hydrogen peroxide (VHP) in adecontamination system, it is necessary to prevent the vaporizedhydrogen peroxide from condensing on the products or articles to bedecontaminated. In a steady state, steady flow vaporized hydrogenperoxide process, the sterilant injection rate, the air flow rate andthe air temperature must be controlled to prevent condensation.According to the present invention, the hydrogen peroxide vaporizersystem is controlled to a desired vaporized hydrogen peroxideconcentration and temperature, to prevent condensation. According to oneaspect of the present invention, the operation of system 10 iscontrolled to maintain the concentration of hydrogen peroxide in an airstream at a dew point temperature that is below the temperature ofarticles to be decontaminated. System 10 is controlled based upon amathematical model that shall now be described.

It is known that the dew point concentration of a water and hydrogenperoxide sterilant is dependant on the temperature of the air—into whichthe sterilant is injected—and the concentration of the water andperoxide in the air. In the case of a steady state, steady flow process,as is used with vaporized hydrogen peroxide decontamination equipment,the dew point concentration is dependant on the injection rate of thesterilant and the temperature and the volumetric flow of air past theinjector.

The concentration of hydrogen peroxide C_(p) in the air stream(mg/liter) can be determined by the following equation:

$\begin{matrix}{C_{p} = {\frac{I*1000}{F*28.32}\left( \frac{P}{100} \right)E}} & (1)\end{matrix}$

-   -   where:    -   I=sterilant injection rate (grams/min)    -   F=air flow rate (actual ft³/min)    -   P=percent of peroxide in sterilant    -   E=vaporizer efficiency (0.90=90%) which is a function of the        amount of hydrogen peroxide broken down in the vaporization        process.

In the equation, the 1000 is a conversion factor for converting grams tomilligrams. The 28.32 is a conversion factor for converting cubic feetto liters.

The concentration of water vapor C_(w) in the air stream (mg/liter) canbe determined by the following equation:

$\begin{matrix}{C_{w} = {{\frac{I*1000}{F*28.32}\left( \frac{100 - P}{100} \right)} + {\frac{I*1000}{F*28.32}\left( \frac{P}{100} \right)\left( {1 - E} \right)\frac{9}{17}} + C_{w,{air}}}} & (2)\end{matrix}$

Hydrogen peroxide breaks down into water and oxygen. Nine-seventeenthsof the catalyzed hydrogen peroxide is converted into water with thebalance being converted to oxygen. This is seen in equation 2 which addsthe water portion of the catalyzed hydrogen peroxide to theconcentration of water seen in the air stream.

C _(w,air)=concentration of water in the air stream flowing into thevaporizer (mg/liter)

From equations (1) and (2), the concentration of water and hydrogenperoxide in the air stream can be determined. The dew point of thehydrogen peroxide is determined based on the following.

It is known that when liquid of a given concentration of H₂O₂ is placedin an enclosure with no initial humidity, the liquid hydrogen peroxideand water will evaporate and reach equilibrium in the enclosure. Theconcentration of the hydrogen peroxide vapor will be lower than hydrogenperoxide concentration found in the liquid. From known sources, such asa book entitled: “Hydrogen Peroxide” by Schumb, Satterfield, & Wentworth©1955, equations and a table provide the relationship between the liquidand gas concentrations for H₂O₂ and water. Within an enclosure, thevapor concentration will reach the saturation point.

Source information is used to determine the saturation point of waterand hydrogen peroxide mixtures in a given volume.

In this respect, the mole fraction of hydrogen peroxide in phase gas(y_(h)) over a hydrogen peroxide-water solution (liquid form) is givenby the following equation.

$\begin{matrix}{y_{h} = {\frac{p_{hg}x_{h}\gamma_{h}}{P} = \frac{p_{hg}x_{h}\gamma_{h}}{\left( {p_{wg}x_{w}\gamma_{w}} \right) + \left( {p_{hg}x_{h}\gamma_{h}} \right)}}} & (3)\end{matrix}$

-   -   where:    -   x_(h)=Mole fraction of hydrogen peroxide in liquid sterilant    -   P=Total vapor pressure of the mix (mm Hg).

The total vapor pressure (P) of the mix is determined by the followingequation.

P=p _(wg) x _(w) γ_(w) +p _(hg)(1−x _(w)) γ_(h)   (4)

-   -   where:    -   p_(wg)=Vapor pressure of water (mm Hg) (see equation below)    -   x_(w)=mole fraction of water    -   p_(hg)=Vapor pressure of hydrogen peroxide (mm Hg) (see equation        below)    -   γ_(w)=Activity coefficient for water

The activity coefficient for water is determined by the followingequation.

$\begin{matrix}{\gamma_{w} = {\exp\left( {\frac{\left( {1 - x_{p}} \right)^{2}}{R\; T}\left\lbrack {B_{o} + {B_{0}\left( {1 - {4x_{w}}} \right)} + {{B_{2}\left( {1 - {2x_{w}}} \right)}\left( {1 - {6x_{w}}} \right)}} \right\rbrack} \right)}} & (5)\end{matrix}$

-   -   where:    -   x_(p)=mole fraction of hydrogen peroxide    -   R=1.987 cal/gmole-K ideal gas constant    -   B₀=Coefficient for calculation of activity coeff.=−1017+0.97*T    -   B₁=Coefficient for calculation of activity coeff.=85    -   B₂=Coefficient for calculation of activity coeff.=13    -   T=Water vapor temperature (K)

The activity coefficient for hydrogen peroxide (γ_(h)) is determined bythe following equation.

$\begin{matrix}{\gamma_{h} = {\exp\left( {\frac{\left( x_{w} \right)^{2}}{R\; T}\left\lbrack {B_{o} + {B_{1}\left( {3 - {4x_{w}}} \right)} + {{B_{2}\left( {1 - {2x_{w}}} \right)}\left( {5 - {6x_{w}}} \right)}} \right\rbrack} \right)}} & (6)\end{matrix}$

The mole fraction of hydrogen peroxide (x_(p)) is determined by thefollowing equation (taken from H2O2.com).

x _(p)=(Percent*MW_(w))/(MW_(p)*(100−Percent)+Percent*MW_(w))

-   -   where:    -   Percent=Percent hydrogen peroxide in gas or liquid form.    -   MW_(w)=Molecular weight of water=18.016 grams/mole.    -   MW_(p)=Molecular weight of hydrogen peroxide=34.016 grams/mole.

The vapor pressure of water is determined using the following equations(from the ASHRAE Fundamentals book). For temperatures above 32° F., thefollowing equation is given:

VP=Exp[(C ₈/(TF+460)]+C ₉ +C ₁₀*(TF+460)+C ₁₁*(TF+460)² +C ₁₂*(TF+460)³+C ₁₃*Log(TF+460))   (8)

-   -   where:    -   VP=Vapor pressure at saturation (psi)    -   TF=Vapor temperature (° F.)    -   C₈=−10440.397    -   C₉=−11.29465    -   C₁₀=−0.027022355    -   C₁₁=−0.00001289036    -   C₁₂=−2.4780681E-09    -   C₁₃=−6.5459673

The vapor pressure of anhydrous hydrogen peroxide is determined by thefollowing equation.

$\begin{matrix}{p_{hg} = 10^{({44.5760 - \frac{4025.3}{T} - {12.996\log \; T} + {0.00446055T}})}} & (9)\end{matrix}$

-   -   where:    -   p_(hg)=Vapor pressure of hydrogen peroxide (mm Hg)    -   T=Vapor temperature (K)

The ideal gas law can be used to calculate the saturation level of thehydrogen peroxide and water vapor components at a given temperature, asshown in reference 2. The ideal gas law is determined by the followingequation.

PV=nRT   (10)

-   -   where:    -   P=Vapor pressure of water and peroxide mix (mm Hg).    -   V=Volume (m³)    -   n=Number of moles    -   R=Universal Gas Constant (0.082 liter-atm/mole-K)    -   T=Temperature of vapor (K)

The saturated concentration of peroxide or water vapor is usually givenin mass per unit volume. Equation (10) can be arranged to determineconcentration as given in equation (11) below.

C=w/V=Mn/V=M×P/(RT)   (11)

-   -   where:    -   C=Saturated Concentration of vapor (mg/liter)    -   w=Mass (mg)    -   V=Volume (liter)    -   M=molecular weight of water or hydrogen peroxide (grams/mole).        -   =34.016 grams/mole for peroxide        -   =18.016 grams/mole for water    -   x=Vapor mole fraction.    -   P=Vapor pressure of water and peroxide mix (mm Hg) from        equations (8) and (9).    -   R=Universal Gas Constant (0.082 liter-atm/mole-K)    -   T=Temperature of vapor (K)

Equation (11) can be solved for the saturated concentration of water(C_(w,sat)) and hydrogen peroxide (C_(h,sat)). The percent of hydrogenperoxide vapor can be calculated using the following equation.

P _(c) =[C _(m)/(C _(p,c) +C _(w,c))]100   (12)

-   -   where:    -   P_(c)=Percent hydrogen peroxide in vapor form.    -   C_(p,c)=Concentration of hydrogen peroxide from equation (11)        (mg/liter)    -   C_(w,e)=Concentration of water from equation (11) (mg/liter)

The percent of hydrogen peroxide in vapor form calculated with equation(12) can be compared to the percent of hydrogen peroxide calculatedusing equations (1) and (2).

P=[C _(p)/(C _(p) +C _(w))]100   (13)

-   -   where:    -   P=Theoretical percent of hydrogen peroxide in air stream.    -   C_(p)& C_(w) are explained in equations (1) and (2) above.

The percent of peroxide calculated in equation (12) should match thatcalculated in equation (13). As explained above, if the percentage ofhydrogen peroxide in the sterilant is used in equation (7), thepercentage found using equation (12) will be too low. The equations canbe forced to produce the correct saturated vapor concentration fromequation (12) by increasing the concentration (Percent) of liquidhydrogen peroxide used in equation (7) until the concentration foundusing equations (12) and (13) match.

Inlet air temperature must be sufficient to vaporize the sterilant andprovide an outlet temperature high enough to prevent condensationdownstream. The required temperature at the inlet to the vaporizer tubeis determined as follows.

The heat required to vaporize the hydrogen peroxide is mostly due to thelatent heat of vaporization for the hydrogen peroxide. To a smallerextent, the sensible heat is needed to heat the liquid sterilant fromroom temperature to vaporization temperature. The heat of vaporization(latent heat) as a function of the concentration of hydrogen peroxide inwater is given in FIG. 10, provided courtesy of H2O2.com.

The latent heat, h_(fg), is given in units of calories per gram. Theunits for h_(fg) can be converted to BTU per gram for 35% peroxide inwater as follows.

$h_{fg} = {{525\frac{cal}{gm}\left( \frac{1\mspace{14mu} {BTU}}{251.9968\mspace{14mu} {cal}} \right)} = {2.083\frac{BTU}{gm}}}$

The heat of vaporization is determined by the following equation.

Q _(wap) =h _(fg)(I)(BTU/min)   (14)

-   -   where:    -   I=sterilant injection rate (grams/min)

The sensible heat required to heat the sterilant from room temperatureto the desired outlet temperature is determined by the followingequation.

Q _(sen) =I·ρ _(ster) ·C _(p,ster)(T ₂ −T _(amb))   (15)

-   -   where:    -   ρ_(ster)=density of the sterilant found from H2O2.com (see        FIG. 11) (gram/ml)    -   C_(p,ster)=specific heat of sterilant found from H2O2.com (see        FIG. 12) (BTU/gram-C)    -   T₂=vaporizer outlet temperature defined by user (C)    -   T_(amb)=ambient temperature of sterilant (C)

FIGS. 11 and 12 are provided courtesy of H2O2.com.

Hot air will be used to vaporize the sterilant. The heat lost by the airstream, Q_(air), is determined by the following equation.

Q _(air) ={dot over (m)}·C _(p)·(T ₁ −T ₂) (BTU/min)   (16)

-   -   where:    -   {dot over (m)}=air mass flow rate=(0.075 lbm/scf)×scfm (lbm/min)    -   C_(p)=specific heat of air at the bulk temperature (BTU/lbm-R)    -   T₁=inlet air temperature (into vaporizer tube) (° F.)    -   T₂=outlet air temperature (out of vaporizer tube) (° F.)

The outlet temperature is determined by knowing the dew point of thesterilant in the air stream using the equations given above. The valuefor Q_(air) is equal to Q_(vap) plus Q_(sen). The only unknown inequation (16) is the inlet temperature. Solving equation (16) for T₁gives:

$\begin{matrix}{T_{1} = {\frac{Q_{vap} + Q_{sen}}{\overset{.}{m} \cdot C_{p}} + T_{2}}} & (17)\end{matrix}$

Referring now to the operation of system 10, a controller (not shown) isprogrammed to allow system 10 to operate in three different modes ofoperation, namely: (1) operating to maintain a desired dew pointtemperature within decontamination chambers 500 a, 500 b, (2) operatingat a fixed rate of sterilant injection, and (3) operating so as to holda desired peroxide concentration. The controller receives input signalsfrom the various sensors throughout system 10. In addition, thecontroller is programmed, based upon the foregoing equations, to controlthe heating elements 298, 352, 752, blower motors 294, 322, 632, 712,and pump motors 124, 324, 428 in accordance with a selected mode ofoperation.

Referring first to the first mode of operation that maintains a specificdew point in the decontamination chambers, certain user inputs arerequired for this mode of operation. Specifically, the user inputs thefollowing: (a) a desired dew point temperature (T_(dp)), (b) a desiredvaporizer outlet temperature, and (c) the percent of hydrogen peroxidein the liquid sterilant.

When vaporized hydrogen peroxide sensor 552 is used, the dew point canbe calculated. When no sensor is available, it may be estimated usingequations (1) and (2) to calculate the water and peroxide concentrations(assuming efficiency is known).

As is known by those skilled in the art, a dew point temperature is thetemperature at which water vapor and hydrogen peroxide vapor in the airbecome saturated and condensation begins. In the context of the presentinvention, the objective of system 10 when operated in the first mode ofoperation is to control the air temperature, air flow, and concentrationof water and vaporized hydrogen peroxide (VHP) in the air stream so asto prevent condensation on articles 12 to be sterilized. As will beappreciated by those skilled in the art, the temperature of articles 12to be sterilized is a factor in determining an actual dew pointtemperature. In the embodiment shown, articles 12 are to be conveyedthrough a decontamination chamber 500A or 500B. The initial temperatureof articles 12 entering chamber 500A or 500B is important in determiningthe desired dew point temperature (T_(dp)). The desired dew pointtemperature is determined based upon the initial temperature of articles12 entering decontamination chamber 500A or 500B. To ensure thatcondensation does not form on articles 12, “the desired dew pointtemperature,” also referred to as a “pre-selected temperature,” inputtedinto the system is preferably a specific number of degrees lower thanthe initial temperatures of articles 12 when entering decontaminationchamber 500A or 500B. In a preferred embodiment, the desired dew pointtemperature is selected to be approximately 30° C. lower than theinitial temperature of articles 12 when entering decontamination chamber500A or 500B. It will, of course, be appreciated that the addedtemperature factor could be increased or decreased, so long as itremains lower than the initial temperature of articles 12.

As will be appreciated by those skilled in the art, the lower thetemperature of articles 12 to be sterilized when entering thedecontamination chamber, the lower the dew point temperature at whichthe water and hydrogen peroxide vapor will condense on articles 12.

The second piece of data inputted by the user is a desired vaporizeroutlet temperature. To a certain extent, these data are also dependenton the physical properties of articles 12 to be decontaminated. In thisrespect, it may be necessary to operate system 10 below a certaintemperature to avoid damaging articles 12.

The third piece of data inputted by the user is the percent of hydrogenperoxide in the liquid sterilant. This information is provided by thesupplier of the liquid sterilant.

Based upon the foregoing inputted information, the system operates inthe first mode of operation as follows.

Initially, both reservoir tanks 132A, 132B in sterilant supply unit 100are preferably filled with liquid sterilant. Liquid sterilant isprovided to the respective tanks by pump 122. Tanks 132A, 132B arepreferably filled to a desired fill level, indicated by level sensor 154in each tank 132A, 132B.

Preferably, one tank 132A or 132B is used to provide liquid sterilant tovaporizer units 300A, 300B at any one time. Once a given tank 132A or132B is depleted of liquid sterilant, liquid sterilant from the othertank 132A or 13213 is then used to supply vaporizer units 300A, 300B. Anempty tank 132A or 132B can be refilled by opening the appropriatevalves 144, 146 to empty tank 132A or 132B and by pumping liquidsterilant from external supply 114 into the empty tank. While an emptytank 132A or 132B is being filled, the other tank 132A or 132B is usedto supply vaporizer units 300A, 300B. Tanks 132A, 132B are dimensionedto allow continued operation of decontaminating system 10 while a tank132A or 132B is being refilled. As a result, a generally continuous flowof sterilant can be provided simultaneously to vaporizers 300A, 300B toallow continuous processing of articles 12.

As illustrated in FIG. 2, liquid sterilant from tanks 132A, 132B aredirected to holding tank 170. Holding tank 170 is dimensioned to allowany gases that may have been released from the liquid sterilant to bevented from supply unit 100 prior to entering vaporizer units 300A,300B. In this respect, it has been found that the outer dimensions ofholding tank 170, being significantly larger than the feed lines andconduit in system 10, allows gas in the liquid sterilant to be releasedand vented, and prevents such gas bubbles or pockets from flowing tovaporizer units 300A, 300B.

As previously indicated, sterilant supply unit 100 is a gravity-feedsystem. To avoid trapping gas bubbles in vaporizer feed line 192, allconduit and piping forming vaporizer feed line 192 from holding tank 170to vaporizer units 300A, 300B have a downward slope such that any gasreleased by the liquid sterilant within vaporizer feed line 192 migratesto holding tank 170 where it can be released through vent line 174.Valve 176 in vent line 174 is controlled by float switch 177.

Referring now to the operation of vaporizer units 300A, 300B as shown inFIG. 3, the operation of vaporizer unit 300A shall now be described, itbeing understood that such description applies also to vaporizer unit300B. The controller of system 10 causes motor 324 to drive blower 322,thereby drawing air through the air-conditioning unit 200 and blowingthe air into vaporizer 360 through vertical conduit 328. The air flowcreated by blower 322 is measured by flow element 332. As indicatedabove, motor 324 is preferably an electrically-controlled variable-speedmotor wherein the air flow created through vaporizer 360 can be adjustedautomatically by the controller. Heating element 352 is energized toheat the air entering vaporizer plenum 364. The output of heatingelement 352 may be adjusted by varying the duty cycle to heating element352. In other words, the temperature of the air flowing into vaporizerplenum 364 can be adjusted by adjusting the output of heater element352.

When system 10 is initially started up, air from blower 322 is forcedthrough plenum 364 and through decontamination chamber 500A. Heated airis blown through system 10 to allow components thereof to heat up untilthe temperature of system 10 stabilizes. Temperature sensors 274, 286,336, 452, 454, 546, 626, 662 and 664 throughout system 10 monitor thetemperature of the air within system 10 and determine when the systemhas reached an equilibrium temperature based upon the input temperatureof heating element 352 as measured by temperature sensor 336.

Once the temperature of system 10 has stabilized, liquid sterilant isinjected into the heated air stream by injector system 410. The amountof sterilant injected into the system is established by the controllerbased upon calculations using the equations set forth above. The initialinjection of liquid sterilant into the heated stream creates a pressureincrease within vaporizer plenum 364 as a result of the liquid sterilantvaporizing in the heated air stream. This increase in pressure withinvaporizer plenum 364 will result in reduced air flow into vaporizer 360.This drop in air flow will be sensed by flow element 332. In accordancewith one aspect of the present invention, the operation of blower motor322 is controlled by the sensed air flow through flow element 332. Basedupon output signals from flow element 332 and sensor 334, the controllerincreases the speed of blower 322 to maintain the desired air flowthrough vaporizer plenum 364 and the downstream units. In this respect,system 10 is self-adjusting to maintain a desired air flow rate throughsystem 10 while vaporized hydrogen peroxide is being generated. Thevaporized hydrogen peroxide from vaporizer unit 360 is conveyed intodecontamination chamber 500A through peroxide feed line 512A. Inaccordance with another embodiment of the present invention, for safetyreasons vaporizer unit 360 is located above decontamination chamber500A, as shown in FIG. 3. In this respect, any hydrogen peroxide notvaporized in vaporizer unit 360 will remain in a liquid state and dripor flow downward into decontamination chamber 500A. The dripping orflowing of liquid hydrogen peroxide into decontamination chamber 500Amay be ascertained from a visual inspection of decontamination chamber500A. If liquid hydrogen peroxide is noticed in decontamination chamber500A, the system is shut down to avoid a hazardous condition.

The vaporized hydrogen peroxide enters manifold 542 where it isdispensed over the articles 12 through nozzles 544. In this respect, aswill be appreciated, articles 12 begin to move through decontaminationchamber 500A once steady-state operation of vaporizer 360 has beenestablished.

As schematically illustrated in the drawings, the vaporized hydrogenperoxide is directed over articles 12 from above. Blower 632 indestroyer unit 600A is energized to draw the vaporized hydrogen peroxideout of decontamination chamber 500A through line 612. Flow element 622provides signals indicative of the flow to blower 632. The controllercontrols the operation of blower 632 so as to balance the air flow outof decontamination chamber 500A with the flow of air through vaporizerplenum 364. The air stream drawn from decontamination chamber 500A isforced through destroyer 642 where the vaporized hydrogen is broken downinto oxygen and water that is exhausted from system 10, as schematicallyillustrated in FIG. 6.

As indicated above, during this mode of operation, i.e., wherein thesystem is controlled to maintain the concentration of water vapor andvaporized hydrogen peroxide in decontamination chamber 500A at a desireddew point temperature, the controller of system 10 constantly monitorsthe various sensors throughout system 10 to ensure that the properamount of liquid hydrogen peroxide sterilant is being injected intoinjection system 410.

In accordance with another aspect of the present invention, system 10monitors and verifies the amount of vaporized hydrogen peroxide producedwithin system 10 in several ways. According to a first method ofmeasuring the vaporized hydrogen peroxide (VHP), system 10 monitors thetemperature drop across destroyer 642 using temperature sensors 662 and664. In this respect, the destruction of vaporized hydrogen peroxideproduces heat. By monitoring the change in temperature across destroyer642, a first indication of the amount of vaporized hydrogen peroxideflowing through the system can be determined.

A second method of measuring and monitoring the vaporized hydrogenperoxide within system 10 is through measurements from vaporizedhydrogen peroxide sensor 462 or 552.

A third method of measuring and monitoring the amount of vaporizedhydrogen peroxide in system 10 is by monitoring the injection rate ofliquid sterilant into injection system 410. In this respect, the outputof mass meter 427 can be monitored to provide an indication of themetered amounts of liquid sterilant to injection system 410. Theperoxide and water concentrations are calculated using equations 1 and2.

A fourth method of measuring and monitoring the amount of vaporizedhydrogen peroxide in system 10 is to monitor the temperature changewithin vaporizer plenum 364. Specifically, temperature sensors 452 and454 within vaporizer plenum 364 are monitored. Just as the destructionof vaporized hydrogen peroxide produces a specific amount of heat perunit mass, so, too, does the vaporization of liquid hydrogen peroxiderequire a specific amount of heat which produces a decrease intemperature. By monitoring the change in temperature in the air streamwithin vaporizer plenum 364, the amount of vaporized hydrogen peroxidein system 10 can be determined.

In accordance with one aspect of the present invention, system 10monitors all four of the foregoing conditions and compares the outputcalculations to each other. If any one of the four monitored parametersis outside an acceptable range of error, system 10 alerts the systemoperator of potential problems.

By continuously monitoring the sensors throughout system 10, theconcentration of water vapor and hydrogen peroxide vapor within the airstream can be maintained at a desired dew point temperature. Since, asindicated above, the desired operating dew point temperature ispreferably approximately 30° C. below the temperatures of articles 12entering the decontamination chamber, condensation on such articles 12can be avoided.

The present invention thus provides a system 10 that can operate tomaintain a specific dew point temperature, to prevent water vapor orvaporized hydrogen peroxide from condensating on articles 12 and, at thesame time, maintain a desired operating temperature so as not to damagearticles 12 to be decontaminated.

Referring now to the second mode of operation, i.e., wherein system 10is held to a predetermined injection rate, the user is required to onceagain input a desired manifold 542 temperature, and the percent ofhydrogen peroxide in the liquid sterilant. In this mode of operation,once a steady-state flow has been established, the injection rate ofinjection system 410 is maintained at a set amount. Air flow through thesystem may increase to maintain a desired operating temperature,however, the injection rate remains constant throughout the operation inthis mode. The dew point is supplied to the user so a determination canbe made if condensation will occur.

In the third mode of operation, i.e., wherein the vaporized hydrogenperoxide concentration is held steady, the user inputs a desiredoperating temperature of the manifold 542. Once steady-state air flowhas been established through the system, liquid hydrogen peroxide isinjected into the air stream. As indicated above, system 10 monitors theamount of vaporized hydrogen peroxide in system 10 and maintains thedesired vaporized hydrogen peroxide concentration by increasing ordecreasing the injection rate of pump 426 of injection system 410.

The control strategy for the first mode of operation is carried out asfollows:

1.) The user inputs the following:

-   -   -   a. The desired dew point temperature (T_(ap))        -   b. The manifold temperature.        -   c. The percent hydrogen peroxide in the liquid sterilant

    -   2.) The following is known:        -   a. Vaporizer efficiency (E) found through testing. (When a            near IR sensor 462 is used, equations 1 and 2 are not            required to determine the concentrations of hydrogen            peroxide and water. When a near IR sensor 462 is not used,            equations 1 and 2 are used to calculate the concentrations            of hydrogen peroxide and water. This calculation requires            that the efficiency of the vaporizer be inputted by the user            into the controller of decontamination system 10.)        -   b. Concentration of water in the air stream out of the            dryer, from vendor data or from testing.

    -   3.) Initially assume the vapor out of the vaporizer will contain        the same percentage of hydrogen peroxide as the liquid        sterilant.

    -   4.) Calculate the mole fraction of hydrogen peroxide (x_(p)) in        the sterilant using equation 7.

    -   5.) Calculate the mole fraction of water in the sterilant,        x_(w)=1−x_(p)

    -   6.) Calculate the activity coefficients using equations 5 and 6        at the dew point temperature input by the user.

    -   7.) Calculate the vapor pressure of water and hydrogen peroxide        using equations 8 and 9 at the dew point temperature input by        the user.

    -   8.) Calculate the total vapor pressure using equation 4.

    -   9.) Determine the mole fraction of hydrogen peroxide in gas over        liquid using equation 3.

    -   10.) Determine if the mole fraction calculated using equation 7        equals that calculated using equation 3.

    -   11.) If the mole fractions don't match within an acceptable        error, iterate the mole fraction of peroxide in the sterilant        (liquid state) and redo steps 5 through 10 above. One of many        iteration techniques may be used to converge to the solution.

    -   12.) If the mole fractions match within the acceptable error,        calculate the saturated concentration of the hydrogen peroxide        (C_(h,sat)) and water (C_(w,sat)) using equation 11.

    -   13.) Calculate the sterilant injection rate from equation 1        using C_(h,sat).

    -   14.) Calculate the concentration of water (C_(w)) using equation        2.

    -   15.) Compare C_(w) with C_(w,sat)

    -   16.) If C_(w) and C_(w,sat) are not equal within an acceptable        error, recalculate the percentage of peroxide (P) using        C_(h,sat) and C_(w): P=C_(h,sat)/(C_(h,sat)+C_(w)) 100 and redo        steps 4 through 15.

    -   17.) If C_(w) and C_(w,sat) are within acceptable error, the        initial injection rate will be set equal to that calculated in        step 15 above.

    -   18.) Calculate the heat of vaporization (Q_(vap)) using equation        14.

    -   19.) Determine the vaporizer inlet air temperature (T₁) using        equation 16.

    -   20.) If the air temperature calculated in step 19 is not too        great for downstream components, the air flow can be established        at T₁ and the peroxide can be injected into the air stream after        the system has reached steady state.

    -   21.) If the air temperature, T₁ is too great for downstream        components, the temperature may be initially set to the maximum        allowable temperature.

    -   22.) The injection rate can then be determined by iterating        until the vaporizer outlet temperature is above the dew point by        the same margin as that between the desired dew point        temperature (T_(dp)) and the desired outlet temperature (T₂).

    -   23.) A gradual step-up process can be continued until the        required dew point (T_(dp)) and outlet (T₂) temperatures are        achieved.

    -   24.) If feedback is provided to the control, the dew point can        be achieved by using the actual concentration of hydrogen        peroxide and water instead of those calculated in equations 1        and 2.

The control strategy for the second mode of operation is set forth asfollows.

-   -   1.) The user inputs the following:        -   a. The desired injection rate        -   b. The manifold temperature.        -   c. The percent hydrogen peroxide in the liquid sterilant    -   2.) The following is known:        -   a. Vaporizer efficiency (E) found through testing (used when            near IR sensor is not used).        -   b. Concentration of water in the air stream out of the            dryer, from vendor data or from testing.    -   3.) The controller calculates and displays a dew point based        upon the injection rate set by the user.    -   4.) The user, knowing the dew point for the inputted injection        rate, can then, if necessary, adjust, i.e., change, the “user        inputs” to avoid condensation on the articles to be        decontaminated. In this respect, in the second mode of        operation, there is no automatic control of the dew point.

The control strategy for the third mode of operation is set forth asfollows.

-   -   1.) The user inputs the following:        -   a. The desired concentration of hydrogen peroxide.        -   b. The manifold temperature.        -   c. The percent hydrogen peroxide in the liquid sterilant.    -   2.) The following is known:        -   1) Vaporizer efficiency (E) found through testing (used when            near IR sensor is not used).        -   2) Concentration of water in the air stream out of the            dryer, from vendor data or from testing.    -   3) The controller calculates and steps-up the injection rate of        the liquid hydrogen peroxide until the desired concentration of        vaporized hydrogen peroxide is achieved.    -   4) The controller calculates and displays the dew point at        desired concentration of hydrogen peroxide

The foregoing description is a specific embodiment of the presentinvention. It should be appreciated that this embodiment is describedfor purposes of illustration only, and that numerous alterations andmodifications may be practiced by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is intendedthat all such modifications and alterations be included insofar as theycome within the scope of the invention as claimed or the equivalentsthereof.

1. An apparatus for decontaminating articles comprised of: adecontamination chamber; a conveyor for conveying articles to bedecontaminated along a first path through said decontamination chamber;a vaporizing unit connected to said decontamination chamber, saidvaporizing unit disposed above said decontamination chamber; a blowerfor conveying a carrier gas through said vaporizing unit and throughsaid decontamination chamber; heating means for heating said carrier gasflowing through said vaporizing unit; a source of liquid hydrogenperoxide fluidly connected to said vaporizing unit; and an injectiondevice for injecting liquid hydrogen peroxide into said vaporizing unit.2. An apparatus as defined in claim 1, wherein said vaporizing unit iscomprised of: an elongated chamber having an inlet port and an outletport, said outlet port fluidly connected to said decontaminationchamber, said outlet port located below said inlet port.
 3. An apparatusas defined in claim 1, wherein said injection device is comprised of: anozzle centrally located in said elongated chamber, said nozzle fluidlycommunicating with said source of liquid hydrogen peroxide and operableto inject a liquid hydrogen peroxide into said elongated chamber as anatomized mist of hydrogen peroxide.
 4. An apparatus as defined in claim1, wherein said heating means is a heater connected to said vaporizingunit.
 5. An apparatus as defined in claim 1, further comprising: adestroyer connected to said decontamination chamber, said destroyer fordestroying hydrogen peroxide in said carrier gas flowing through saiddestroyer; and a blower disposed between said decontamination chamberand said destroyer for conveying said carrier gas from saiddecontamination chamber to said destroyer.
 6. An apparatus as defined inclaim 1, further comprising: an air conditioning unit connected to saidvaporizing unit, said air conditioning unit comprised of: a chamber; afilter connected to said chamber for removing contaminants from saidcarrier gas flowing through said chamber; a cooling device connected tosaid chamber for cooling said carrier gas flowing through said chamber;a regeneration conduit connected at one end to said chamber; a blowerfor conveying a portion of said carrier gas from said chamber throughsaid regeneration conduit; heating means for heating said portion ofsaid carrier gas flowing through said regeneration conduit; and adesiccant element connected to said chamber and said regenerationconduit for removing moisture from said carrier gas flowing through saidchamber.
 7. An apparatus as defined in claim 6, wherein said desiccantelement is rotatable about an axis such that portions of said desiccantelement are moveable between said chamber and said regeneration conduit.8. An apparatus as defined in claim 1, further comprising: a reservoirassembly connected to said source of liquid hydrogen peroxide and saidvaporizing unit, said reservoir assembly comprised of: a first storagetank; a second storage tank, said first storage tank and said secondstorage tank connected to said source of hydrogen peroxide; a collectiontank connected to said first storage tank and said second storage tank,said collection tank also connected to said vaporizing unit; valve meansfor selectively fluidly communicating said first storage tank and saidsecond storage tank with said collection tank and for selectivelyfluidly communicating said first storage tank and said second storagetank with said source of liquid hydrogen peroxide; a vent line connectedat one end to said collection tank and a second end of said vent linedisposed at a location above a top of said first storage tank and saidsecond storage tank; and a vent valve disposed in said vent line tocontrol flow therethrough.
 9. An apparatus as defined in claim 8,further comprising: pumping means for pumping said liquid hydrogenperoxide from said source of liquid hydrogen peroxide to said firststorage tank and said second storage tank.
 10. An apparatus as definedin claim 8, wherein said collection tank is located above saidvaporizing unit.
 11. An apparatus as defined in claim 1, furthercomprising: an aeration unit connected to said decontamination chamber,said aeration unit for removing contaminates from a gas flowing throughsaid air aeration unit and said decontamination chamber, said aerationunit comprised of: a conduit connected at one end to saiddecontamination chamber; a blower for conveying said gas through saidconduit to said decontamination chamber; a filter for removingcontaminates from said gas flowing through said conduit; and heatingmeans for heating said gas flowing through said conduit.
 12. Anapparatus as defined in claim 11, further comprising: a branch conduitconnected at one end to said vaporizing unit and at another end to saidconduit at a location upstream of said filter; and valve means forselectively fluidly connecting said vaporizing unit to said filter andsaid decontamination chamber.
 13. An apparatus for decontaminatingarticles in a decontamination chamber having a reservoir assemblycomprised of: a first storage tank connected to a source of hydrogenperoxide; a second storage tank connected to a source of hydrogenperoxide; a collection tank connected to said first storage tank andsaid second storage tank, said collection tank also connected to avaporizing unit; valve means for selectively fluidly communicating saidfirst storage tank and said second storage tank with said collectiontank and for selectively fluidly communicating said first storage tankand said second storage tank with said source of liquid hydrogenperoxide; a vent line connected at one end to said collection tank and asecond end of said vent line disposed at a location above a top of saidfirst storage tank and said second storage tank; and a vent valvedisposed in said vent line to control flow therethrough.
 14. Anapparatus as defined in claim 13, further comprising: pumping means forpumping said liquid hydrogen peroxide from said source of liquidhydrogen peroxide to said first storage tank and said second storagetank.